The present invention relates to an electrostatic capacitive or piezoelectric pressure sensor and a method of manufacturing the same and, more particularly, to a bonding structure and bonding method for a sensor chip and sensor package employed when electrodes of the sensor chip are extracted from the lower side of the sensor chip.
As a conventional pressure sensor, an electrostatic capacitive pressure sensor is known. The electrostatic capacitive pressure sensor has a substrate with a recess, a diaphragm supported on a substrate at its periphery and arranged on the recess, a stationary electrode formed on the bottom surface of the recess, and a movable electrode formed on the diaphragm to oppose the stationary electrode. In the pressure sensor having this arrangement, when the diaphragm deforms upon reception of an external pressure, the distance between the movable and stationary electrodes changes to change the electrostatic capacitance between them. The pressure applied to the diaphragm is measured on the basis of this change in electrostatic capacitance.
As another pressure sensor, a piezoelectric pressure sensor is known. The piezoelectric pressure sensor has, in place of an electrode, a strain gauge with a piezoresistive effect on a semiconductor diaphragm. The strain gauge is deformed by a pressure applied to the diaphragm. The pressure is measured by detecting a change in resistance of the strain gauge produced by the piezoresistive effect.
To measure a pressure by using the pressure sensor described above, as shown in FIG. 6, a sensor chip 23 is mounted on a cylindrical glass base 22 in a cylindrical metal package 21 sealed by a corrosion-resistant diaphragm 24, and a sealed liquid 25 such as silicone oil is sealed in the metal package 21. The pressure is transmitted to the sensor chip 23 by this structure. The electrical connection between the sensor chip 23 and the outside is realized by connecting electrode extraction pins 26 hermetically sealed with glass and electrodes formed on the upper surface of the sensor chip 23 with wires 27.
With the arrangement as shown in FIG. 6, since the volume of the sealed liquid 25 changes in accordance with a temperature change, an error occurs in transmission of the pressure, making it difficult to measure the pressure at high precision. If the diaphragm 24 is torn and the sealed liquid 25 leaks, a measurement target liquid (gas) is contaminated by the sealed liquid 25. Thus, this arrangement is difficult to use for sanitary applications.
In order to solve these problems, the sealed liquid may be eliminated. In this case, as the sensor chip comes into direct contact with the measurement target liquid, corrosion of the sensor chip and physical impact applied to the sensor chip pose problems. For this reason, electrodes and wires cannot be formed on the upper surface of the chip, and the electrodes are extracted from the lower side of the sensor chip.
In the conventional pressure sensor, however, if the sensor chip is fixed, the electrodes cannot be extracted from the lower side of the sensor chip. More specifically, when the sensor chip extends to the lower surface of the metal package and the electrodes are extracted from the lower side of the sensor chip, a stress is likely to occur in the bonding portion between the sensor chip and the seal surface of the package. For this reason, the diaphragm of the sensor chip need be set away from the seal surface, leading to an increase in size of the sensor.
In the pressure sensor, a thermal stress from the metal package should not be transmitted to the sensor chip as much as possible. The measuring method shown in FIG. 6 realizes this by mounting the sensor chip 23 on the glass base 22 and bonding the glass base 22 to the metal package 21. With this method, the number of manufacturing steps increases. Also, the number of bonding surfaces increases, thereby degrading the yield.
In the pressure sensor shown in FIG. 6, since the electrode extraction pins 26 are fixed to the metal package 21 with a glass hermetic seal 27, distances d1 and d2 between the electrode extraction pins 26 cannot be decreased because holes must be formed. Also, an insulating distance (the size of the glass hermetic seal 27) d3 cannot be decreased.
It is an object of the present invention to provide a pressure sensor which, in a structure where electrodes are extracted from the lower side of a sensor chip, the sensor chip can be fixed and the electrodes can be extracted simultaneously while improving the yield, and a method of manufacturing the same.
In order to achieve the above object, according to the present invention, there is provided a pressure sensor comprising a cylindrical sensor package, a glass base seal-bonded to an inner surface of the sensor package to close a space in the sensor package, a sensor chip mounted on the glass base and having electrodes and a metal bonding portion on a surface thereof opposing the glass base, the bonding portion being die-bonded to a surface of the glass base, and lead members arranged to oppose the electrodes and buried to extend through the glass base, one end of each of the lead members exposed from the surface of the glass surface being electrically bonded to a corresponding one of the electrodes.